5. Grand Theft Auto Series!
4. Knights of the Old Republic! (Nice story with you choosing your own destiny)
3. Metal Gear Solid 1-2! (sad to say this is the only mgs on the pc)
2. Blizzard Games! (another score?!)
1. Oblivion! (Every mod will give you at least 1 + hour of gameplay!) (love this game!)
1. Starcraft I/II
2. Diablo I/II
3. Call of Duty 4 (never played this [Probably never will] but it seems very underrated)
4. Half Life Series (never played this [Probably never will] but it seems very popular)
5. Bioshock (never played this either)
1. Doom
2. Doom
3. Doom
4. Doom
5. Doom
6. Castle Wolfeinstein
7. Duke Nukem
8. Civilization
9. Sim City
10. Lemmings
11. Might and Magic
12. Diablo
13. Quake
That's all I've got off the top of my head.
Don't just jot down the games people play today and call them the "Best PC games of all times".
If I see a "best" list with Crysis or Bioshock in it I'm not reading any further. It is good, maybe really good, but to compare it with a legend like Doom? Lunacy.